The present invention relates to an automatic leveling system for adjusting optical axes of atutomotive headlamps based on a pitch angle of a vehicle, and more particularly to an automatic leveling system for vertically adjusting optical axes of headlamps based on a pitch angle of a stationary vehicle.
A headlamp of the type used in an automatic leveling system is constructed such that a reflector with a light source securely inserted therein is supported to tilt about a horizontal tilting axis relative to a lamp body. An actuator is used to tilt the optical axis of the reflector (a headlamp) about the horizontal tilting axis.
A conventional automatic leveling system is constituted by a pitch angle detecting means, a vehicle speed sensor, and a control part for controlling the driving of actuators based on detection signals from the detecting means and the sensor, which are provided on a vehicle. The optical axes of headlamps (reflectors) are adjusted to remain in a certain position relative to the surface of a road at all times.
The conventional automatic leveling system automatically levels the headlamps in real-time, such as when a vehicle posture changes because of acceleration or deceleration or when the load is loaded or unloaded, or the passengers get in or out of the vehicle. This increases the operations of the actuators, leading to greater power consumption. Moreover, a high durability is required for driving mechanism components such as motors and gears, which leads to greater production costs.
To provide an automatic leveling system that can reduce the frequency of use of actuators and that is inexpensive and durable, an automatic leveling system was proposed (Japanese Patent Application No.10-274859) in which actuators are driven at predetermined intervals (ten second intervals) while a vehicle is at a stop.
However, while the actuators of the above automatic leveling system are controlled based on a pitch angle detected during a predetermined interval time, if an interval control coincides with the start of the vehicle, automatic leveling cannot be properly performed. The problem is described with reference to FIG. 6.
FIG. 6 is a chart showing changes in vehicle speed and vehicle posture from the start of the vehicle until it reaches a constant running speed. As shown in the chart, it takes a predetermined length of time (T) before the vehicle actually starts running after an accelerator pedal is depressed. In other words, the vehicle speed starts increasing after the predetermined length of time (T) has elapsed. Because of this, the vehicle sensor detects the start of the vehicle at a predetermined start detection delay time T after the accelerator pedal is depressed.
As to the vehicle posture, when the accelerator pedal is depressed, a rear part of the vehicle first lowers and the vehicle continues to remain in that state. That is, when the vehicle sensor detects the start of the vehicle (when a control part detects the start of the vehicle based on an output from the vehicle sensor), the rear part of the vehicle is in a lowered position or, alternatively, the front part of the vehicle is in a raised position.
Because of this, as shown in FIG. 6, there may be a case where the timing of an interval control falls within (T), a time period between the lowering of the rear part of the vehicle by the depression of the accelerator pedal and the detection of the start of the vehicle by the vehicle speed sensor. A vehicle pitch angle for use for interval control in this case is improper because the pitch angle is calculated based on the vehicle""s lowered position. The control part is forced to control the actuators based on the improper pitch angle data.
An object of the present invention is to provide an automatic leveling system for automotive headlamps that is inexpensive and that can provide a longer service life by reducing the frequency of use of actuators by controlling the actuators at predetermined intervals. Another object of the invention is to provide an automatic leveling system adapted to operate properly even if the timing of interval control coincides with the start of the vehicle.
According to a first embodiment of the invention, an automatic leveling system for automotive headlamps comprises headlamps optical axes adapted to tilt vertically relative to a body of a vehicle by driving actuators, a control means for controlling the driving of the actuators, a vehicle speed detecting means for detecting speeds of the vehicle, a pitch angle detecting means for detecting pitch angles of the vehicle and a storage part for storing pitch angle data of the vehicle detected by the pitch angle detecting means. The control means controls the actuators based on the pitch angle data detected by the pitch angle detecting means such that the optical axes of the headlamps are tilted in a certain tilted angle relative to a road surface.
The storage part is configured to store a plurality of data detected at predetermined time intervals.
The control means is configured to control the actuators based on pitch angle data not affected by a change in posture of the vehicle when the vehicle is started and the interval control is carried out substantially at the same time. The control means controls the actuators at predetermined intervals based on the latest pitch angle data.
Additionally, according to a second embodiment of the invention, an automatic leveling system for automotive headlamps is provided such that the start of the vehicle is detected by the vehicle speed detecting means within a predetermined set time after an interval control of the actuators is carried out. The control means determines that the interval control and the start of the vehicle substantially coincide with each other.
Furthermore, according to a third embodiment of the invention, an automatic leveling system for automotive headlamps is provided such that the predetermined set time, which is used to determine whether the interval control and the start of the vehicle coincide with each other, isequal to or longer than a vehicle start detection delay time, which is a time from an accelerator pedal is depressed until the vehicle speed detecting means detects the start of the vehicle.
Pitch angle data generated while the vehicle is at a stop are more accurate than pitch angle data generated while the vehicle is running because there are less disturbing factors when the vehicle is stationary. Since the actuators is controlled based on the more accurate pitch angle data, a more accurate automatic leveling can be provided with the former pitch angle data.
In addition, since the control of the actuators is limited to a certain time interval, the frequency at which the actuators are driven is reduced to that extent. Thus, power consumption is reduced and the wear on the driving mechanism is reduced.
Moreover, the start of the vehicle may be detected by the vehicle speed sensor. If an interval control coincides with the start of the vehicle the actuators may be driven based on an improper pitch angle. A proper automatic leveling can be effected by controlling the actuators based on a proper pitch angle obtained before the depression of the accelerator pedal.
Referring to FIG. 6, a proper automatic leveling process is described in detail. If an interval control of the actuators happens substantially at the same time that the vehicle starts,that is, if an interval control falls within a vehicle start detection delay time T (from the time the accelerator pedal is depressed until the vehicle speed sensor detects the start of the vehicle), a pitch angle used for this specific interval control is that detected by the pitch angle detection means when the interval control occurs. Hence, there may be a risk that the pitch angle data so detected include data generated when the vehicle is lowered when it is about to start. Therefore, the pitch angle data may not be necessarily proper for use. That is, the actuators (automatic leveling) may be driven based on improper pitch angle data.
To address this, instead of a pitch angle detected when the vehicle changes posture, a pitch angle detected prior to the vehicle start detection delay time T (pitch angle data designated by reference character A in FIG. 6 which are detected before the accelerator pedal is depressed) may be used.
Although it varies depending on the type of vehicle, in general, a time of 1 to 3 seconds elapse before the vehicle actually starts. Because of this, it is desirable to set the vehicle start detection delay time to range from 1 to 3 seconds. Whether or not the interval control is carried out substantially at the same time that the vehicle starts can easily be determined if the predetermined set time described in the second embodiment of the invention is set to fall within the range of the vehicle start detection delay time (1 to 3 seconds).
In addition, according to a fourth embodiment of the invention, an automatic leveling system for automotive headlamps is provided such that one or more interval controls have been carried out before an interval control that coincides with the start of the vehicle. Pitch angle data used for an interval control preceding the interval control coinciding with the start of the vehicle, can be used for correcting the headlamp leveling. If an interval control is carried out for the first time, pitch angle data detected just previous to the depression of the accelerator pedal while the vehicle is at a stop, can be used to correct the headlamp leveling. If an interval control is carried out for the first time and if there is no stored pitch angle data detected previously to the depression of the accelerator pedal, the actuators are prevented from being driven.
If a number of interval controls have been carried out, a control based on the latest pitch angle data while the vehicle is at a stop is made possible by using the pitch angle data used for the preceding interval control (the pitch angle data detected while the vehicle is at a stop).
In addition, if the interval control is carried out for the first time, because there is no pitch angle data that are used for the preceding interval control, a control based on the proper pitch angle data is made possible by using pitch angle data detected just prior to the depression of the accelerator pedal (pitch angle data detected before the vehicle speed detection means detects the start of the vehicle, for example, before a predetermined start detection delay time).
Moreover, the actuator is prevented from being driven if the interval control is carried out for the first time and that a time during which the vehicle is stopped is shorter than the predetermined start detection delay time (assuming that there is no pitch angle data preceding the depression of the accelerator pedal). According to a fifth embodiment of the invention, an automatic leveling system for automotive headlamps has a storage part configured such that older pitch angle data are replaced with newer pitch angle data in the order stored, when latest pitch angle data are received so that data can be updated.
Pitch angle data of the predetermined time can be taken out atany time, and the capacity of the storage part does not have to be expanded. According to a sixth embodiment of the invention, an automatic leveling system for automotive headlamps controls the actuators, provided that the headlamps are illuminated.
The actuators are not driven as long as the headlamps are not illuminated, and thus the number of times the actuators are operated is reduced by that extent. Therefore, power consumption can be reduced and the wear on the constituent members of the driving mechanism can be reduced. According to a seventh embodiment of the invention, an automatic leveling system for automotive headlamps configures an interval at which the actuators are driven such that the interval becomes longer than a maximum driving time of the actuators, which is needed to perform a single leveling operation.
If an interval between the previous control and the next control is shorter than the maximum driving time of the actuators, the actuators start the next operation before a target value is reached. In this situation, the actuators will be driven more often and may have their service life reduced. However, according to the construction as set forth in the seventh embodiment of the invention, the actuators are driven in the next control after the actuators have reached their target value in the previous control. Thus, the number of times the actuators are driven is reduced by that extent, and the service life of the actuators is not reduced.
In addition, a change in the pitch angle within the time interval from the previous control until the next control can be omitted without triggering the driving of the actuators by extending the interval at which the actuators are driven. Alternatively, all the operations within the interval can be converged on the driving of the actuators in the next control, and therefore the number of times the actuators is driven is reduced by such an extent.
Additionally, pitch angle data of the vehicle, detected by the pitch angle detection means, are taken into the control part at all times for arithmetic operation as control data, even during intervals between driving operations of the actuators. By using all the pitch angle data that are taken into the control part as control data, many pitch angles can be used as control data. Thus, a proper leveling of the headlamps is attained in association with the detection of the accurate posture (pitch angle) of the vehicle.
Moreover, an automatic leveling system for automotive headlamps, is provided such that while the vehicle is running, when the vehicle runs in a stable running condition over a predetermined length of time where the vehicle speed is equal to or faster than a predetermined value, and the acceleration is equal to or less than a predetermined value, the driving of the actuators is controlled based on pitch angle data resulting during the stable running period. In this case, leveling (optical axes correction) based on the pitch angle data resulting during the stable running condition can function to correct the leveling (optical axes correction) based on pitch angle data resulting while the vehicle is improperly stopped such as along a slope or on a curb.